text:
Are there any documented example usages of film (ie, film film, not video or digital) for in-flight entertainment?
Regarding this excellent question: What was the inflight entertainment in the early seventies?
There's a mention that the "TRANSCOM 8mm film cassette" (that was film-film, ie the plastic stuff you can see-through, not video tape) was used on some planes.
I've found all the references to this on the WWW are poor references copying each other with no details (but I may be missing something).

Can anyone find literally an image of film-projector technology being used for in-flight entertainment?
Are there any specific references / image examples to the "TRANSCOM 8mm film cassette"
What year was about the last year film projection technology was used (if it was ever used?)

Or indeed -- memories of these things, even better! Cheers.

I know film projectors were definitely used on early 747s - converting part of the passenger area into a theater is part of the design. I was able to dig up the photo below showing the projector mechanism, which is pretty impressive to look at.

I'm not sure whose system that is, but it looks like a 35mm projector so it probably predates the TRANSCOM cassettes.
Can't help you with #2 or #3 though.

incredible find!  wow!  thanks...

The video link is dead. Can you dig again? :)

@Farhan Unfortunately that was the only source for the movie I knew of (that's why I grabbed the screen capture, I was afraid it might go dead on us one day).  I'm not sure if it's just "unavailable" for maintenance or if it's actually gone dead for good, so I'll leave the link for now in the hope that it comes back. If it's still dead in a week or two I'll adjust the answer to just reference the photo. (Stupid link rot!)


text:
What is this aircraft with a crew member in an exposed nose compartment?

Possibly from around 1935, possibly involving one of the two airplane-supplying-powers in the Spanish Civil war.
(Seen in a documentary about the 20th century inter-war era...it's only onscreen for a few frames.)
(It looks like one of the fantastical, almost-plausible air vehicles seen in Ghibli films!)

BTW those relatively inexpensively-made documentaries tend to just shove in any-old bits of stock footage or other odds and ends of footage they find: the images often don't precisely relate to the topic the narrator is going on about, so, the milieu info mentioned is not a lock.

What documentary was this shown on? Do you know the title of the series?

@Freiheit , sure - look simply at the top of the TV screen in the photo !!  Of the streaminmg services, "Amazon Prime" I believe.  you can get the time mark from the thermometer at bottom.  Thanks!

Studio Ghibli was strongly inspired by the many fantastical, almost-plausible air vehicles built during the interwar period.

indeed @mark (I'm a big fan!)

@Fattie I have changed the title because "Bloke" is a colloqualism, which may well be unclear to international users. I think this title better reflects what you're asking and helps with correct indexing should someone else be searching for something similar.

For what its worth I think the change in title is a good move. I only clicked on the question because "Whats this type with a bloke in the nose" made no sense and I was curious as to what the question actually was. I'm a native English speaker (UK) and the meaning was not clear at all.

I believe this is a Dornier Do 18 flying boat / patrol bomber. The cockpit with its central piece of glass is quite distinctive. It entered service in 1938, and doesn't appear to have been involved in the Spanish Civil War.
There is a short film on YouTube which has the same sequence as the documentary you saw. Looks like it was part of a movie which featured the Do.18; the cockpit fills with smoke and the "bloke in the nose" (the gunner) starts to look for somewhere to land is what I think is going on.
The Dornier 18 has the distinction of being the first German aircraft to fall to British gunfire in WW2: on September 26th 1939 a Do.18 was felled by a Blackburn Skua.
Since there is some astonishment at the position of the forward position, it's worth noting that it was extremely common for inter-war military flying boats to allow someone to be stationed up front in this manner, for both reconnaissance and gunnery, and for ropes and other maritime uses. For instance most of the designs for medium and large seaplanes from Short Brothers and Supermarine have such a front station in this period.
There are too many to list, but since you mention Studio Ghibli you may want to reference Italian seaplane designs by CANT (e.g. Model 25, Z.501), Macchi (e.g. M.18, M.24) and Savoia-Marchetti (e.g. SM.62, SM.78) from where a lot of inspiration was derived.
I took a look at the documentary you saw, the aircraft registration is 6L+E05. So this was a Do 18D-1 which entered service in June 1938 in Travemünde and ended its days two years later in Putzig (Puck, Poland) after an engine fire on takeoff.

source

Thanks !!  My God, what a place to ride during water landing/takeoff.  Does anyone know if the "bloke" could actually move within the aircraft - some sort of passage? Or did he just climb up in there before takeoff ... and that's it?

This schematic http://www.airwar.ru/image/idop/sww2/do18/do18-3.gif seems to indicate that there was a door to a passage that led to the crew compartment. Most flying boats do have such a thing; the bow compartment is where the anchor is stowed. To drop anchor, a crewmember passes through the bulkhead door to get there. In Grummans, for instance, you would crawl through doors at the pilots' feet.

Personally I think it would be absolutely fantastic to have a go up front. (Although possibly not in the Baltic where a number of Do.18s were stationed.)

The PBY also has a nose gunner there, it's enclosed unless the gun is in use, then the gunner has to open the front window and roof to mount and man the gun (fully enclosed gun turrets were introduced later in the aircraft's service).

Awesomely, I see the Do18 actually also had another bloke, outdoors, behind the wings!! Awesome!  Thanks for the further info.

The flaming-roll-of-toilet-paper heraldry really gilds the lily.

@PartyArk In peace time? Absolutely. But sitting there while chased by an enemy fighter would be most unpleasant.

@Roger the flying loo roll is, surprisingly, supposed to be a fist. It's the emblem of 2/KuFlGr 406  which operated Do 18s from 1937 to 1942 - https://www.asisbiz.com/Luftwaffe/kflgr406.html

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text:
Is GPS considered to be a navigational facility for the purposes of Ops Spec C055?
For 14 CFR 119 certificate holders, Alternate Airport IFR Weather Minimums are prescribed by Operations Specification (Ops Spec) C055, specifically Table 1 of that specification.
Below is a generic example of Table 1:

The wording in this table is understandable in the context of a traditional, ground-based navigational facilities such as NDB, VOR, or ILS providing an approach. For a simple example, if an airport has an operational VOR navigational facility providing an approach, that satisfies the requirements of the first row with the result that the 400 ft ceiling and 1 sm visibility minimums might apply.
However, some §119 certificate holders are authorized to conduct GPS approaches and to use GPS approaches in determining alternate airport weather minimums. For these operators, the table needs further clarification as it does not provide a framework to derive alternate airport weather minimums based on the GPS approaches that are otherwise authorized to be used for that purpose.
No such clarification seems to be given anywhere else in C055 or elsewhere in the Ops Specs.
How do GPS approaches fit into table 1? Does the Global Positioning System (GPS) constitute a navigational "facility" for the purposes of Table 1? If so, does it constitute a single navigational facility, thereby satisfying the requirements of the first row, just as if a single VOR provided an instrument approach?
Is there guidance provided elsewhere on this?

Yes, a GPS approach can satisfy the criteria of a navigational facility for the purposes of Table 1 in Ops Spec C055.
The FAA gives the following guidance in Notice 8900.218, Alternate Airport IFR Weather Minimums:

G. 5) Planning for use of GPS-based IAP must be based on a single navigational
  facility when determining the approach facility configuration in Table 1, even if there are two or more RNAV (GPS) approaches to different suitable runways.

This guidance doesn't go to the length of explicitly including GPS in the definition of "navigational facility". However, it does mean that GPS-based IAP can be understood to substitute for a single navigational facility, thereby satisfying the criteria of the first row of Table 1.

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text:
What FAA rules govern tethered, outdoor UAV flight?
This question is concerning the possibility of operating an Unmanned Aerial Vehicle (UAV) outdoors—a commercially available quadcopter, for example—but with the distinction of operating the UAV while tethered.
In this letter of legal interpretation, the FAA states, that:

The FAA has repeatedly affirmed it's position that any vehicle
  designed for tethered operations only, and not for "free flight",
  should be considered a kite.

An applicable kite (over 5 lbs., etc) would be subject to 14 CFR 101.
However, any UAVs which were originally designed for free flight would clearly not meet the "kite" definition—even if operated tethered, since the original design was for "free flight" and not tethered operations only.
This is my primary question: If an UAV were attached to a tether and so operated, would that UAV remain subject to all legal requirements regarding the operation of UAVs?
Additionally, I would be interested in the following:
Is there a letter of legal interpretation from the FAA on this matter, or any other regulatory or guidance material that I am not aware of?
Are there any rules governing tethered aircraft flight, in general, apart from 14 CFR 101?

Not really definitive at all, but I have read articles about tethered flying cars which were allowed to be tested in tethered flight only because the tether allowed them to bypass certification rules needed for free flight.  They too were obviously designed for free flight.  (Of course, this could also have something to do with insurance rather than just FAA rules, who knows??)

If you altered the UAV in such a way as to make it permanently "designed for tethered operations only" then I'd think yes, but if there is anything we know as pilots it's that the U.S. aviation laws love to be overly open to interpretation.

@Lnafziger Pure speculation but I suspect there's a big difference between "There's only one of these things and, hey, we'd really like it to fly free but we decided to tether it for testing" and "Anybody can buy one of these from the store and fly it free but I've decided to tether mine."

@DavidRicherby Maybe!  But then again, once it is tethered a whole host of safety concerns go away, so maybe not!

You said tethered UAV and I immediately thought, "are we asking about kite flying?"  Guess not... ;)

The FAA's rulemaking document for UAVs says that tethered UAVs are not considered balloons or kites (thanks to Steve V. for finding it):

[...] a small unmanned aircraft that uses powered systems
  for actions such as propulsion or steering is not a balloon or kite
  subject to part 101

And:

[...] the FAA notes that the definition of small UAS in this rule includes
  tethered powered small UAS

So a UAV is not a kite and it is subject to all the general UAV regulations (I think they'll be published as 14 CFR 107 at some point). There are also a couple of FAA sources that say that if a tethered aircraft of any type is capable of free flight then all the usual regulations apply. This is from the interpretation you quoted:

Since 1957, the FAA has repeatedly affirmed its position that any
  vehicle designed for tethered operations only, and not for "free
  flight" should be considered a kite.In contrast, if an ultralight vehicle is designed to be tethered only
  until it achieves a predetermined altitude and is released for free
  flight, that ultralight is an aircraft regulated under part 103
  during the entire operation.

There's also a very clear statement on tethered balloons:

Free and Tethered Flight Considerations. If a balloon is considered an aircraft under one circumstance (such as free flight),
  it must still be considered an aircraft under other operating
  circumstances, including tethered flight. Tethered balloons are
  considered aircraft, and must be operated in compliance with all
  construction, certification, airworthiness, registration, and
  operating regulations applicable to aircraft.

That comment about "operating circumstances" seems to be the general FAA position on tethered aircraft.

See also the Final Rule for part 107 (Page 80):  Based on these definitions, a small unmanned aircraft that uses powered systems for actions such as propulsion or steering is not a balloon or kite... and the FAA notes that the definition of small UAS in this rule includes tethered powered small UAS (page 94)

@SteveV. Nice find, thanks! I've updated my answer based on that information

Somewhere I have a LOI on tethered operation of a helicopter...

After consideration, I thought I would add that one may wish to request a LOI (letter of interpretation) regarding tethered flight.  If you can bound your problem (where, purpose, etc.) you might get a favorable interpretation.

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text:
In simple terms, what are LNAV, VNAV, and Baro-VNAV approaches?
In simple words, what are LNAV, VNAV, and BARO-NAV?
Are they all precision approaches and will they cancel the traditional approaches?

Related: What is “required navigation performance” or “RNP”?. See also this Boeing document.

Also related: What is the difference between LNAV/VNAV and LPV minimums on an RNAV approach? and Is LPV considered a precision approach?.

authors: ابراهیم باباپوری


text:
Are all US airline aircraft certified into known ice?
Are all  US airline aircraft certified for flying into known icing (FIKI) conditions?
I assume all the large (100+ PAX) aircraft come FIKI certified from the design stage?
What's the largest passenger aircraft that would be non-FIKI certified?

Title 14 CFR part 121.321 regulates scheduled airline operations in icing conditions.  It requires airframe ice protection systems in order to operate in "conditions conductive to airframe icing", which they define as:

visible moisture at or below a static air temperature of 5 °C or a total air temperature of 10 °C, unless the approved Airplane Flight Manual provides another definition.

This essentially means that any airline that can operate in IMC is going to be subject to this requirement unless they have very niche operations at low altitudes in warm lattitudes where they can stay below the 10 C level when in IMC.
Aircraft operated by airlines that operate in IMC at temperatures colder than 10 C must either have an ice detection system or a means of detecting the first formation of ice on the airframe and then activate ice protection systems or they must, in the absence of detection, always operate their ice protection when operation in conditions conductive to airframe icing.
For smaller on-demand operations operating under part 135, 14 CFR 135.227 regulates flight into icing conditions.  This regulation requires that any airplance flying into forecast icing (IFR only) or known icing conditions (VFR or IFR) has functioning de-ice or anti-ice protection.  This means a 135 operation ferrying passengers from Miami into the Bahamas probably doesn't have to worry about this, but a IFR 135 operation anywhere it gets cold probably does.
For non-121 and non-135 operations in airplanes with 20 passenger seats or more, the applicable regulation is 14 CFR 125.221 and reads exactly like the part 135 regulation.
Summary
Combined, parts 121, 125 and 135 regulate the majority of commercial operations.   The requirements of part 121 realistically mean that any airplane suitable for scheduled airline operations is equipped with ice protection.  Part 135 can utilize a broader range of aircraft and while ice protection is not required it is quite limiting for the operation if it is not present (no flight into known or forecast icing conditions under IFR).
This means that all airline aircraft (part 121) are certified for FIKI but not all passenger airplanes (operated under part 125 or 135) are certified for FIKI (and cannot operate in those conditions if not equipped).
Regs

§121.321   Operations in icing.
(a) When operating in conditions conducive to airframe icing, compliance must be shown with paragraph (a)(1), or (2), or (3) of this section.
(1) The airplane must be equipped with a certificated primary airframe ice detection system.
(i) The airframe ice protection system must be activated automatically, or manually by the flightcrew, when the primary ice detection system indicates activation is necessary.
...
(2) Visual cues of the first sign of ice formation anywhere on the airplane and a certificated advisory airframe ice detection system must be provided.
(i) The airframe ice protection system must be activated when any of the visual cues are observed or when the advisory airframe ice detection system indicates activation is necessary, whichever occurs first.
...
(3) If the airplane is not equipped to comply with the provisions of paragraph (a)(1) or (2) of this section, then the following apply:
(i) When operating in conditions conducive to airframe icing, the airframe ice protection system must be activated prior to, and operated during, the following phases of flight:
...
(ii) During any other phase of flight, the airframe ice protection system must be activated and operated at the first sign of ice formation anywhere on the airplane, unless the Airplane Flight Manual specifies that the airframe ice protection system should not be used or provides other operational instructions.

§135.227   Icing conditions: Operating limitations.
(c) No pilot may fly under IFR into known or forecast light or moderate icing conditions or under VFR into known light or moderate icing conditions, unless—
(1) The aircraft has functioning deicing or anti-icing equipment protecting each rotor blade, propeller, windshield, wing, stabilizing or control surface, and each airspeed, altimeter, rate of climb, or flight attitude instrument system;
(2) The airplane has ice protection provisions that meet section 34 of appendix A of this part; or
(3) The airplane meets transport category airplane type certification provisions, including the requirements for certification for flight in icing conditions.


text:
Which airplane designs have the greatest longevity?
What airplane designs have been around the longest, from first flight through last retirement from active commercial or military service?
My guess is that the DC-3 will win, since it has been around since before WW II and is still in service, although there are enough other designs out there I'm not familiar with that I'll be interested to see where I may be wrong on that. (Russian designs come to mind as an obvious source of possibilities.)
Can anything out there beat the DC-3? What's the runner up?
(The wikipedia page on the DC-3 says its first flight was December 17, 1935.)

@Farhan - similar, but distinct in that I'm thinking less about production timeframes, than design logevity. That site has some interesting leads, though. (Looks like he deleted his comment; site posted was https://en.m.wikipedia.org/wiki/List_of_most-produced_aircraft)

Yes, I deleted my comment as I noticed answers started to come in. So I thought I might not have completely understood the question.

There is already an older plane listed, but the PBY Catalina first flew in March 1935 and there are still models being flown.

If you are asking for airplane you already have answers, if you are looking for aircraft, ballon basic design is unchanged since centuries. That will be your oldest designed aircraft. Airplanes are a little bit more than one century old

I'm not sure to fully understand the question. Do replicas count? Are you looking for the oldest aircraft still maintained in flying condition?

The answers below are good, but a good bet for the longest combat aircraft might be the B-52. It first flew in 1955 and is scheduled to last into the 2040s, though with the difficulty of retiring aircraft lately it may very well make it to its hundredth birthday in service (some aging MIG fighters from the early 50s are also in service with third-world air forces, but they are unlikely to last another 25+ years)

@SSumner - if this question comes up in 2050, I wouldn't bet against the B-52 (although something like the C-130 or B-747 or 737 be viable by then as well), but given the strong preference at SE for answers rather than speculations & discussions, I think limiting the question to what has that longevity today, rather than what may hold the title in the future, may be best.

@RalphJ - sure, and that's why I made it a comment rather than an answer (though the 737 and 747 are a full 10 years younger than the B-52, and the C-130 some 3 years younger - I mistyped the BUFF's first flight)

@SSumner -  All true, but those 3 are all still in production 50+ years later, with two of the production lines still going strong. So even if the BUFF makes it to 100, it may be one of the others that takes the last crew back home from the Boneyard. We'll check back in another 40 years or so and see how things have turned out!

This is a community-wiki mashup of the other answers - I thought a table would be useful.

Date Introduced
Aircraft Type
Commercial Service (2015)

1909
Bleriot XI
Flown by Shuttleworth collection UK, entrance fee.

1932
JU-52
Sight seeing flights by Ju-Air, Switzerland.

1932
Tiger Moth
Flight experiences, e.g. Cheltenham UK.

1934
Dragon Rapide
Sight seeing flights, London.

1935
DC-3
Many still in airline passenger or cargo service (Nothern Canada, Alaska, Venezuela); some re-engined to turboprop engines.

1935
PBY Catalina
Still used in aerial firefighting role.

1938
Piper Cub
Many still in private/GA use and in flight schools.

1945
Beech Bonanza
Date is from first flight, model is still produced and a common private/GA airplane

1947
AN-2
Still in widespread use in 2020.

1952
B-52
76 still in service with USAF. Projected service to 2045?

1952
Tu-95
In service with Russian air force. Projected service to 2040?

Seems reasonable to point out that all those older than the DC-3 are one, two, three flying examples -- and there are still dozens, if not hundreds of DC-3 in day-to-day service around the world.

@ZeissIkon According to Wikipedia there are about 250 Tiger Moths still flying.

@EricS Okay.  As trainers?  I know of a few doing effectively barnstorming.

@EricS, the important part about DC-3 is that it is still in airline service, not as flight experience because it is old, but because it is so well suited to operating to remote poorly maintained unpaved airstrips.

@JanHudec According to Wikipedia the Tiger Moth is still occasionally used as a primary trainer. https://en.wikipedia.org/wiki/De_Havilland_Tiger_Moth?wprov=sfti1

If any commercial or military service will do then there are a few designs which are older.
There's a de Havilland Dragon Rapide still in commercial service doing air tours around London, that's first flight was in 1934. The Noorduyn Norseman is still used for air tours and cargo work and it was first flown a month before the DC3. The Ford Trimotor was introduced in 1925 and I think there's still one or two doing tours.
Apart from tours the DC3 is still the one I'd think of as still doing really serious service.

There are at least two Ford Trimotor  still offering tours.  http://www.eaa.org/en/eaa/flight-experiences/fly-the-ford-eaa-ford-tri-motor-airplane-tour

The Shuttleworth Collection, at Old Warden aerodrome in Great Britain, has a flyable Bleriot XI which was built in 1909 and served at a flight school into the Thirties. It is still regularly displayed in flight. You might argue that this is no commercial service, but to witness the display, you need to buy a ticket, and ticket sales help to support the collection. So I enter it as a contender here.
Having flown first in 1932, the Ju-52 is also older than the DC-3 or even the Dragon Rapide. Several are still in commercial service - you can book scheduled sight-seeing flights with the Swiss operator Ju-Air. Ju-Air's three Ju-52 served from 1939 to 1982 in the Swiss Air Force. Wikipedia has an exhaustive list of current Ju-52 operators.

The CASA license-built Spanish version of the Ju52 was in service with the Spanish air force until 1974 or 75. It was a safe and conveniently slow plane for parachute drop training train. I myself flew many times in it during my military service...

The legendary Piper Cub which was used as a trainer during WWII and first flew in 1938 is still a popular plane and although not by Piper is still made in some form of variants today. I dont think its in service any more (at least as far as I know) but there are still loads of them flying.

The USAF B-52 first flew in 1952, stopped production in 1962, is still a frontline bomber, and is projected to continue service until 2045
http://en.wikipedia.org/wiki/Boeing_B-52_Stratofortress

Ju-52 started in 1931 and in 2018 - after 87 years - was still used for a commercial passenger transportation (nostalgic flights but between the two different airports like Duebendorf to Locarno all the way over the Alps and not just circular tours), by the Duebendorf based airline (Switzerland).
Unfortunately these flights were suspended after the 79 year old aircraft crashed in 2018. However the airline expects to resume the service in 2021 (source).
Older designs may serve for longer as they parts have less (or no any) strict life limits as set by the manufacturer.


text:
Why has the maximum service ceiling of Boeing and Airbus products remained about the same for 30 years?
When Boeing introduced the 747-100 in 1969, its maximum ceiling was 45,100 feet; half a century later, when Boeing introduced the 777x, its maximum ceiling was 43,100 feet.
Similarly, the maximum ceiling of the Airbus A300, introduced in 1972, is 40,000 feet, while the ceiling of the A350, introduced 2 years ago, is 43,100 feet.
Given the all the other advances in aircraft design between the past and current generation of airliners, why has the ceiling remained unchanged?

The tropopause has remained about the same.

@digitgopher That was also my first thought when I saw the this question. I would rather disagree with the assertion that Boeing products have a maximum service ceiling in the tropopause, though. Boeing commercial airliners, yes. But Boeing has some other products which tend to fly a bit higher than that. :)

@reirab: But did these extra products increase the Boeing ceiling in the last 30 years :-)

@mins Well, the last one does at least have that as a design goal. :)

Also, I'm not quite sure why this has an RO vote. It seems to be an exact dupe of the other question (well, at least if you exclude those other Boeing products. ;) )

Mainly, the optimum cruise altitude is where thrust and lift requirements for both take-off and cruise balance well. An additional benefit is the colder air which increases the efficiency of heat engines. Since this helpful drop in temperature ceases once the aircraft climbs above the tropopause, the benefits of flying higher increase most below the tropopause.
With increasing flight altitude, the airliner needs:

Bigger engines to create the needed thrust in thinner air
Bigger wings to create the needed lift

With the wings, the size of the tailplanes will also grow; this effect alone likely will weigh more than the beefing up of the fuselage structure for the increased cabin pressure. Flying higher will make almost all parts bigger and heavier.
Note that Mach 0.85 is a hard limit for efficient flight; airliners cannot compensate for lower density by flying faster. The only way to allow higher flight levels is to attach bigger wings and tails.
Another consideration is Breguet's formula: Jet aircraft have their optimum cruise lift coefficient at a value of $c_L = \sqrt{0.6\cdot c_{D0}\cdot\pi\cdot AR\cdot\epsilon}$, if we assume the thrust of high-bypass-ratio engines to vary with speed proportional to $v^{-0.5}$, which is a reasonable assumption. This means the airliner cannot fly higher by flying at a higher lift coefficient: This would decrease efficiency.
(Nomenclature: $c_{D0}$ = zero-lift drag, $AR$ = wing aspect ratio, $\epsilon$ = span efficiency)
With the wing size and the engines needed for flight at Mach 0.82 in the tropopause (Mach 0.85 is really not as efficient; follow the link to find out why this is the quoted cruise speed for long-range airliners), the take-off distance is quite reasonable and approximately matches the airports which had been defined by NATO during the cold war. Flying any higher into the stratosphere would increase the aircraft's mass due to bigger engines and wings, but would not incur the efficiency gains of increasing cruise altitude in the troposphere, where temperature drops with altitude.
Conversely, picking a lower design cruise altitude would allow to make both wings and engines smaller, but this would translate into:

Higher take-off and landing speeds, and critical speeds during take-off due to the smaller wing,
Lower take-off acceleration due to smaller engines,
For twins: Not enough thrust during take-off when one engine fails,
Lower climb speeds, so it would take longer to reach cruise altitude, and
Not fully taking advantage of the cold air up in the tropopause.

Designing for a lower cruise altitude would translate into much longer runways and less efficient flight overall.
Designing for cruise in the tropopause is simply the sweet spot for airliner designers where all conditions match well and produce a balanced outcome.

The aircraft are optimized to fly at a particular altitude, which has not changed over the years. There are multiple reasons for this:

The higher you go, the less denser air becomes; So, for flying at higher altitude (i.e. for same lift), the aircraft has to fly at higher angle of attack (increasing drag; the wing will stall at some altitude anyway) or greater speed (requiring more thrust due to increased drag).
As the altitude increases, the thrust produced by the engine falls, and at some point, the thrust produced isn't just enough for flight. This is the most important limitation for service ceiling.
In commercial airliners, the cabin pressure altitude is held constant (usually ~8000 ft ISA) and the differential pressure will cause stresses on the fuselage; As the air density decreases with altitude, this stress increases and strengthening the structure will increase weight, resulting in poor performance.
In case of transport aircraft, the service ceiling may sometimes be limited by the maximum altitude from which they can descend to 14,000 ft in less than a specified time (4 min). Commercial airliners are usually limited by this certification altitude.
Even if the engine thrust is increased and the aircraft can fly at higher altitudes (at more speed), at some point another limitation will manifest itself- The air being accelerated over the wing will reach supersonic speeds and form shock waves, leading to a paradoxical situation where you can neither increase the speed (which will increase drag due to shock waves) nor decrease speed (which will stall the aircraft).

However, some aircraft have flown at higher altitudes where their design was  optimal. For example, Concorde flew at ~55,000 ft due to lower drag and consequential heating of the airframe from supersonic speeds.
As an interesting (and unrelated) side note, any aircraft, however powerful, cannot fly above certain altitude as the atmosphere becomes too thin and it would have to fly faster than orbital velocity to generate necessary lift. This is taken as the point where outer space begins and is called the Kármán line


text:
What are the largest airports in terms of size, gates, and stands?
What is the largest airport in terms of:

Size of developed area?
Size of all terminal area?
Total number of gates?
Total number of gates + remote stands?

According to InsiderMonkey DFW (Dallas/Fort Worth International Airport) is the largest at 4360 hectares.
According to Wikipedia DXB (Dubai International Airport) has the largest terminal in terms of floorspace at 1,713,000 m2 (18,440,000 sq ft) with a volume of approximately 10.0 million m³ (360 million cu ft)
According to this forum ATL (Hartsfield-Jackson Atlanta International Airport) has 206 gates
Can't find this one

Depending on how you define "developed area", Edwards Air Force Base could surpass DFW.  It's got a lot of runways, and some of them are rather large (eg. 17/35 is about 400 hectares for the runway surface alone).

In addition to its massive number of gates, ATL is also the world's largest by passenger throughput and by flight operations.

@Mark - "developed area" of Edwards typically does not include the dry lakebeds and their runways (which are marked more for convenience than anything; Edwards is the primary government test-flight facility in part because the lakebed is flat enough to land practically anywhere). Being fair to commercial installations, areas of the base that don't have a counterpart on commercial installations, such as barracks/base housing, should be excluded as well. That dramatically reduces Edwards' "developed size".

I nominate Davis Monthan Air Force Base as the winner in category 4. Not for the number of gates, it is the number of remote stands that does it.

In English for us Americanian types.

most of those planes looks half demoed

@ratchetfreak they are...

the boneyard counts as a bunch of remote stands? that's like saying a cemetery counts as housing.


text:
What is the production status of the Pipistrel Panthera as of March 2017?
What is the production status of the Pipistrel Panthera? They had plans to start production in 2016/2017 but nothing new has been published in the last two years.

Great question.  I have high hopes that it will be the much needed competitor to Cirrus.  It looks almost too good to be true.

I may have more news on that next week from Sun 'n Fun 2017.  Pipistrel will be an exhibitor at the show and may have a Panthera prototype on display.
Currently the Panthera is planned to be released as an experimental kit and may be type certified at some point in the future.
I know the program has suffered some setbacks, including an increase of empty weight by some 200 lbs.  New aircraft development is never fast nor without complications.
The Panthera does look intriguing - 200 KIAS on 10 GPH with good, stable flight characteristics and modern avionics, BRS parachute, etc.  I want to take it for a demo flight when production examples become available.


text:
What are those thin magenta lines on the Sectional / Terminal Area Chart near Death Valley?
Due west of KLAS and Death Valley are a large number of MOAs and Restricted areas. On the sectional and terminal area charts, there are thin magenta lines snaking over some of the mountain tops.
What do those lines represent? They don't seem to be a mode C veil of any sort, and the legend doesn't otherwise mention a thin magenta line without spikes.

Those lines denote areas of the MOA which have altitude exclusions different from what is listed on the chart's MOA table. In this case:

MOA Excludes Airspace 3000' AGL & Below

Notice the same style magenta lines are drawn in circles around airports in the MOA which also have the same style remark excluding a specific portion of the airspace.


text:
What are the advantages and disadvantages of a delta wing compared to a swept wing?
What advantage does a delta wing have over a swept wing with high AR for supersonic flight? And what disadvantage does a delta wing have over a swept wing with high AR for transonic flight?
The Concorde is made to cruise at supersonic speed--delta wings.
Most commercial airliner--swept wing with high AR.
Would you design a supersonic airplane with the conventional airliner swept wings? On the other hand, would you design a transonic flight with delta wings?

See the comparison of wing types, and more specifically, delta wings on commercial airliners.

Benefits of a delta wing:

Due to the large root chord, a delta wing combines low relative wing thickness with a sufficiently thick wing spar for a lightweight structure. Since a low relative thickness keeps wave drag down (a drag component which occurs only in supersonic flow), this makes delta wings especially attractive for supersonic aircraft.
The large root chord gives the delta wing a high internal fuel volume even at a low relative thickness.
The large root chord also provides it with a large surface area which helps to bring the minimum speed of the aircraft down.
With sufficient leading edge sweep, a delta wing produces vortex lift, so flow separation can be turned into a means of increasing lift.
A delta wing is naturally stable in pitch, therefore it does not require a separate tail surface.

Drawbacks of a delta wing:

The large wing area causes more viscous drag for the same amount of lift compared to a high aspect ratio wing. Swept wings have a better lift-to-drag ratio (L/D) than delta wings.
High-lift devices like fowler flaps are hard to integrate into delta wings. The higher relative thickness of regular airliner wings allows to integrate large flaps more easily, and the rearward location of the trailing edge of a delta wing will produce intolerable pitching moments if such flaps would be deflected.
Vortex lift at high angle of attack produces considerably more drag than a comparatively sized conventional wing, so a delta wing airplane will bleed off speed in tight turns more than a conventional airplane.

Generally, the moderately swept high aspect ratio wings of subsonic airliners are ideal for flight at high subsonic Mach numbers. Delta wings are superior only in supersonic flight, and due to their good low speed characteristics they offer the best overall compromise for supersonic aircraft.

North American XB-70 in flight, a classical delta wing design (picture source). Note the canard wing, which has little sweep and a low aspect ratio: This kind of wing is ideal for supersonic flight, provided it has a low relative thickness. The main wing of the XB-70 is a delta wing to keep the take-off and landing speeds relatively low and offers the best compromise of low and high speed characteristics. Also, the wing tips could be deflected downwards to improve directional stability at supersonic speed and to improve L/D by using the waverider effect.

The wings of both the Boeing 787 (top, picture source) and the Airbus A350 (bottom, picture source) show their powerful high-lift devices in these pictures, which allow them to fly with less than half the wing area of a comparable delta wing aircraft. Also, the lower surface area translates into lower drag at high flight speed, and the higher possible wing span helps to reduce induced drag, making those wings far superior for efficient flight at high subsonic speed.

With regards to flaps, delta wings typically make use of their natural stability at high angles of attack to perform a flaring maneuver as an alternative to flaps. Like flaps, a flaring delta wing is both high lift and high drag. This is part of the reason for the drooping nose design of the concorde. The one downside to flaring vs flaps is that you can use your elevator to correct pitching changes when deploying flaps but since you're using elevators for flaring you can't do that. Therefore flaring needs to be done gently if you don't want to end up gaining altitude by mistake.

@slebetman: Also, a delta wing experiences much more ground effect during landing. But still, the maximum lift coefficient is maybe 40% of that of a fowler-flapped wing, so area-wise it is much less efficient. Also, look at the outer wing of the SR-71: It is pulling around a lot of extra drag from the drooped leading edge just to make sure the plane doesn't roll off during flare. But leading edge devices just won't fit into such a thin wing.

The fuel argument isn't meaningful in the supersonic and high transonic case, though, because the cross sectional area is essentially fixed with the Sears-Haack body if I'm not mistaken. I suppose the distribution of volume could be advantageous if you want to keep fuel away from the cabin and maybe there are situations where you'd want to distribute the fuel weight to a wing.

@Gus: Since the delta wing helps to stretch out the thickness distribution, it allows a bigger cross section. The Sears-Haak body of a delta winged aircraft is larger - just compare a F-106 or Dassault Mirage to the EE Lightning! The delta wing is larger but the local gradients are the same. On the Lightning they had to add (as a belly tank) what they cut out from the wing initially. Wouldn't it be better to have that volume contribute lift as well?

And what about stalling charcteristics of a delta wing? Are they favourable (pitch down etc.) or not?

@Konrad: Plain delta wing: No, strong pitchup after stall. Cranked delta (with less sweep on the outer wing, like X-31): Neutral, as required for post-stall maneuvering. Here is a bit more on the issue.

@PeterKämpf sorry to bother. I heard something about "delta wings fighters are not good at continuously turning, as it bleeds out speed faster". Any truth to that? and how would you explain it?

@eliu Better to ask a new question. In short: The small span of a delta means more induced drag at high lift which slows the airplane down. I could add this as another disadvantage.

Delta wing advantages

Can fly at high angles of attack, which that's why fighter jets use a delta wing to fly at very high angles of attack
Provides good amount of drag for landing. On landing you need drag and that's the purpose of flaps is to increase drag and lift and you can make the flaps a little bit smaller

Delta wing disadvantages

Lots of drag, which is caused by vortex lift that a delta wing uses instead of conventional lift. Instead of just suffering drag from a wing tip vortex you suffer even more with 2 extra vortices that form on a delta wing.

With a swept wing you reduce drag by decreasing the lift. The problem with that type of wing at supersonic speeds is that you surfer from wave shock drag. Wave shock drag forms when air on top of the wing exceeds the speed of sound. Even at subsonic speeds that a 787 travels at you suffer from wave shock drag. Air is moving so fast on top of the wing at subsonic speeds that it causes the air to break the sound barrier. If you try to fly a swept wing at supersonic speeds your aircraft is really going to suffer from wave shock drag and any faster speeds could result in the whole plane splitting apart and is very serious. A delta wing doesn't have a slope on top of the wing like a swept wing does so the air doesn't travel any faster than the aircraft does. The reason airliners use swept wings is to reduce the lift to reduce the amount of high pressure air that can rotate around the wingtip. The swept wings reduce wake vortex and wake vortex can actually decrease an aircrafts lift and you want as much lift as possible. The major companies that build airliners main focus is to decrease drag. With a supersonic aircraft your main focus is to reach supersonic speeds and aren't designed to reduce drag. So you wouldn't design a supersonic aircraft that has swept wings, but you would design it with delta wings.

Hi Ethan.  Sorry to say but your answer is rambling, contains many inaccuracies and misunderstandings and is not salvageable.  We are all aware that you are only 14 and we admire your thirst for knowledge and your dreams.  This site though expects high quality accurate answers and does not distinguish who the poster is.  If Peter Kampf posted a wrong answer, it would be downvoted.  This is how Stack Exchange works.  If you clean my car for me, and you spend 1 hour doing it but do a lousy job or you spend 5 minutes doing it and do a great job, which one am I going to like the most?

@Simon "If Peter Kampf posted a wrong answer, it would be downvoted." can you pass by chat?


text:
How can I mount my iPhone 6 in the cockpit to record my flights?
I am a student pilot, and would like to record my training flights to look back on. I do not have a Go-Pro, and do not want to fork over the money for one. I do however, own an iPhone 6, that has a pretty good camera. I was wondering if anyone had some ideas as to how I could mount my phone in order to record my flights? I thought maybe a suction mount would be best, as I could mount it behind my shoulder on the back of the glass cockpit (Cessna 152)
If possible, it would be better if it could record my control inputs throughout the flight. Please let me know if anyone has found a working solution in the past.

video shooting of your pilot skill will distract from your duty, better have a person to do that? if there is any space for another person to do it from behind co-pilot seat?

Sorry guys, I must clarify! I mentioned mounting the phone in my original post, so that I could attach it in some way to the interior fo the cockpit, preferrably the glass roof of the Cessna, therefore not requiring me to film, rather mounting it to a monopod. And by my control inputs, I mean having the phone in a position to view my inputs to the instrument panel, so not infront  of me.

I fail to understand what you want to film, but I were you I would try using (double faced) adhesif tape.

Re suction mount: note they rely on pressure difference which becomes less as you climb.

Sell you iphone and buy nokia and a digital camera

Good point DeltaLima, I did not think of that!

Isn't mounting any non-rated equipment anywhere in the cockpit against the regulations?

@yo' - with the amount of in cockpit footage on YouTube, either it isn't or there are a lot of people getting/about-to-be busted

@yo' No, permanently installing something or other otherwise altering the aircraft itself generally needs approval. However, temporarily attaching something within the cockpit (e.g., by clips, velcro, adhesive, etc.) generally does not need approval.

UPDATE  9/4/2017
I'm thrilled this post has been so helpful for so many people. As such, I wanted to  update it with more details and more current links in case people are interested. Enjoy!

You could have a lot of fun, and get a lot out of reviewing the footage of your lessons. I'd look into a suction cup mount as you are already considering. When buying a suction cup mount, make sure you get one that is "beefier" than you expect you need. Whatever you do, make sure you share your videos online, your video might even get someone else interested in aviation!
Below are the details of doing what you asked. You might be able to buy a used, older model gopro for a comparable price - but I'd actually argue your phone is probably a better option.
What to buy:
(this all actually gets kind of expensive, but is still cheaper than buying a go pro and accessories)
Must have:
To get GoPro functionality from your iphone, you'd need a mount and a case:

http://amzn.to/1ZQDx7q (Optrix Super Sucker Mount)
http://amzn.to/1MyN1uc (Case)

This is a mount that mimics the functionality of a go-pro mount. It also let's you know if pressure is dropping in the suction cup as you climb.
If you ever feel brave enough you could even stick this to your wing!

http://amzn.to/1GmeYbU

The view angle probably is not wide enough. This inexpensive kit will apply a wide angle to your iphone. I'd make sure your case/mount doesn't preclude using one of these.
Best alternative camera to GoPro:

http://amzn.to/2vZsQEx (Garmin Ultra Virb 30)

I love the aviation data overlay of this camera. It works very well and helps debriefing a lot. I personally prefer this over my GoPro because it includes that data.
Best GoPro options:

http://amzn.to/2xJKn67 (GoPro Hero5 Black)

4k resolution @ 30FPS, 12MP quality is great. I use this mainly for wing mounted shots.

http://amzn.to/2eDiQi3 (GoPro Hero5 Session)

The nice thing about the session series is they are small and super simple to operate. I use this camera to point inside the cabin, on the side windows. It is nice because it doesn't block as much of my view outside, even in a mount on suction cups.
Important Accessories:

http://amzn.to/1ZQERqT (Zoom H1)

I use this to record ATC/Headset audio. It is easy to have it recorded to its own device and lets me have better control over the audio recordings than if it was part of a video file. The audio is oftentimes more useful than the video alone, especially with your instructor explaining things to you. Having a separate device also reduces your point of failure risk if you have a camera battery die.

http://amzn.to/2wAg29z (Headset cable to record audio)

You need this cable to "grab" audio from your headset jack to record it to a camera or external recorder. (Note- the Garmin Virb 30 Aviation bundle includes this)

http://amzn.to/2wAo1Uh (External Battery)

You will be running out of battery fast if you record HD video for any length of time. This external charger will keep you from running out of battery.

ND (Prop) Filters (remove the weird prop strobing from your footage)

(Note- the Garmin Virb 30 Aviation bundle includes this)

http://amzn.to/2xJhxm9 (GoPro Hero5 Black ND Filter)
http://amzn.to/2exTIFG (GoPro Hero5 Session ND Filter)

Placement:
The best place to put it would be between the seats on the ceiling pointing landscape style towards the instrument panel. This would give you a view of all of your instruments and maybe even a bit of the horizon. At first, we all struggle to use the horizon as a reference instead of instruments, so putting the camera close to head level might help develop a good sight picture.

Here's a video using the angle I am referring to.
Unless you set up a second camera, you are unlikely to get rudder input on film. This video shows a good example of that angle, but might be impossible while getting dual instruction.

Video showing rudder control input on takeoff
Words of caution:

Make sure your filming doesn't distract you. This is really serious and not something to shrug off. Remember, you don't want the FAA to have footage to shove in your face of you being reckless.
Make sure you don't damage the aircraft with the mount. The windshields in particular are vulnerable to being squeezed out of shape from the pressure in the suction cup, especially if they are hot. I have seen some indented windshields recently due to gopro mounts, which makes it very hard to get a normal sight picture (imagine looking through a fun house mirror).
UPDATE
Another issue I recently saw was a result of someone using this camera: http://amzn.to/1oos68G. The camera has a built in rare earth magnet which made mounting it very easy. The problem was, it was impacting the magnetic compass - so be aware if you get a magnetic mount to make sure your compass is not affected by it being placed in the cockpit! When attached to the overhead speaker we saw no visible impact on the compass, but worth keeping an eye on.

Take a look on youtube at some popular pilot channels to see how they record. From there, you can pick your favorite angles and splice a film together.

Wow, thanks heaps man, best answer I've found! Thanks again


text:
How far should commercial jets be from each other when on the runway or while departing?
Does anyone know how far should a commercial jet (787,777,etc...) be away from each other in runway or in process of taking off?
Are there public resources that I can look up?

Are you talking about how far "behind each other" or "next to each other" ? While reading your title, I thought you were talking about side-by-side simultaneous takeoff.

The FAA's Federal Aviation Regulations (FAR's) are all publicly listed here.
There are a wide variety of cases to consider on the ground and during departure but you can find a lot of the regulations/guidelines in this document.
For example here is the case for wake turbulance seperation,

Separate a small aircraft weighing 12,500 lbs. or less taking off from an intersection on the same runway (same or opposite direction
  takeoff) behind a departing small aircraft weighing more than 12,500
  lbs. by ensuring that the aircraft does not start takeoff roll until
  at least 3 minutes after the preceding aircraft has taken off.
Separate a small aircraft taking off from an intersection on the same runway (same or opposite direction takeoff) behind a departing
  large aircraft (except B757) by ensuring that the aircraft does not
  start takeoff roll until at least 3 minutes after the preceding
  aircraft has taken off.

That is just one example, the document is very lengthy and covers a lot of cases, you should be able to find what you are looking for. You should also keep in mind that things like weather and local airport policies will cause the regulations to vary a bit. For example a local noise abatement may cause the seperation/interval timing to be larger than required to adhear to the noise abatement.
That covers mostly what ATC will see and do, you can take a look at this document for how pilots look at departure procedures.


text:
What is the lift to empty weight ratio of some popular modern helicopters?
What is the lift to empty weight ratio of some popular modern helicopters?

This question cannot be answered as it is. It's too broad for one thing, and you are asking for people's opinions rather than facts. Plus, I don't have any idea what you are actually asking.

Your question about pros and cons is mostly a legal and financial one, not an aviation one. We might be able to help with technical issues for your prototype, though, if you have any specific questions.

I have edited my question. Thank you.

I have edited your question further to really focus on the aviation part of the question, making it more likely you get a good answer. You can rollback my edit if you disagree.

Popular according to whom? Popular for what purpose?

From Prouty: Helicopter Performance, Stability and Control: the example helicopter that is referenced throughout the book, to illustrate the equations used and computations made.
The rotor thrust T is a function of blade geometry and number of blades. The blade is just a rotating wing and maximum thrust is a function of the lift coefficient $C_l$ of the blade profile. Rotor thrust is also a function of rotor disc area and number of blades.
The example helicopter has the following characteristics:

Design gross weight = 20,000 lb
Minimum operating weight = 10,700 lb
Main rotor radius = 30 ft
Blade geometry: chord = 2 ft, airfoil = NACA0012, 4 blades

The average lift coefficient of the blade is computed on page 18 as $C_l$ = 0.52 at sea level, for the design gross weight. NACA 0012 has a maximum $C_l$ of 1.2, which makes the maximum rotor thrust at sea level:
$$ T_{max} = 20,000 * 1.2 / 0.52 = 46,153 lb $$
So maximum lift divided by minimum operating weight is 46,153/10,700 = 4.3
Since NACA0012 and 0015 can still be found in many helicopters, this would be the general order of magnitude for popular type helicopters. A max lift/empty weight of about 4. Further variations are due to disk loading: higher disk loading means a higher $C_l$ to lift off.


text:
Does an aircraft like the Airbus A-320 have external sensors to detect damage to the aircraft?
I read a news item recently . According to the article, the wingtip of an Airbus A-320 collided with the left wing of an A-330 while on the taxiway at Mumbai airport. The A-320 (VT-IFP) experience a damaged sharklet. The collision was observed by a passenger and then shared with the aircraft staff (flight attendants I guess) who informed the captain. The plane was led to a hangar, passengers de-boarded and sent on other plane/s by the airline.
What I want to know is: aren't there any sensors which can detect an impact and give/share that information to the pilot? I do understand that the airplane takes a lot of jerk and movement during takeoff and landing as well as during turbulence.
But when damage as such as the one described above happens, why isn't there some automated system that could inform the pilot instead of having to rely on a passenger's keen eyes?

VT-IFP is the identifier for the specific aircraft

You can put everywhere sensors which send a simple-keep alive signal over cables, but you will receive just a lot of false-positives and add a lot of weight. It is just simpler, to build better planes. For this kind of detection you will need some sort of fault tolerant advanced composite material with a generic interface, which can detects it's status and report it itself. And even then, should they able to report "scratches"?

Related

VT-IFP is the aircraft's registration. The prefix VT indicates that it was registered in India.

This is related to an answer I gave here about why aircraft typically do not have mirrors and external cameras.
Short answer: yes aircraft do have sensors to detect damage, but not the kind of damage you're talking about.
Long answer: to design or decide what sensors to put on the aircraft and where, we have to get started with failure modes. There are at least a million way for components to fail, however, some failure are more likely to occur than others.
Do we have sensors which detect failures / abnormal situations? We do! We have sensors for control surfaces, hydraulics, gears, tire pressure, cabin pressure, engine temperature, oil pressure etc.
Here is an image of one of the cockpit screens on a Boeing:

(source)
OK, so why not more sensors?
Because sensors can fail. Now that would be a nightmare to troubleshoot: the sensor says the right outer landing light is not illuminated. Is that true? Let me exit the aircraft and take a look......
It turns out that:

Many failure modes are "internal", e.g. a valve malfunctioning. They are invisible on the exterior of an aircraft.
Aircraft rarely collide with any other objects.
Relying on visual indication is actually a good thing, because it is reliable and it's free.
Building an array of sensors covering each skin on the aircraft would be extremely complex, the construction cost would be high and the system would be heavy.
Sensors are just another component of the system. The more sensors, the more likely something will fail. At some point one has to trust the underlying component to function without relying on system indications.

Perhaps this is the kind of system you have in mind:

(Screenshot of "Stealth" (2005), 01:01:11)
Nah, that's just Hollywood artistic license.

You may complete your (quite good) answer by expanding the failure modes you are talking about.

Note that the plural of "aircraft" is "aircraft".

The one collision damage sensor that airplanes sometimes have is a tailstrike sensor, to detect the tail hitting the runway during takeoff or landing.


text:
How is oil distributed through the engine in a wet sump system?
A wet oil sump is within the engine crankcase. However, how is the oil distributed throughout the engine and all the other magical parts? I know for a dry oil sump, it's with a oil pump which holds the oil from a reservoir, but for wet oil sump, how?

There is still an oil pump if that is what you are asking...

There's an oil pump in within the crankcase that pumps the oil around?

Yes, by definition it is "wet" meaning it is submerged in the oil, but it is still a pump.

The pump is submerged in the oil...now that is news to me. Thanks.

The crank can fling oil around as well.

@acpilot You can still have splash lubrication in dry-sump engines too (in fact you usually will unless the engine was specifically designed to avoid any splashing & is instead equipped with separate oilers to spray the pistons and other parts that usually only get splash lubrication). There's a lot less splashing though, and consequently less power loss from the crankshaft dragging through the oil.

The short answer is "The same way as in a dry sump system." – There is an oil pump which sucks oil out of the oil pan and forces it through the engine oil galleries under pressure.
Wet and dry sump oil systems only really differ in where they store "extra" oil.

Wet Sump Systems
In a wet sump system the oil is stored in the oil pan under the engine. The oil pan serves as both the oil tank (holding the supply of lubricating oil) and the oil sump (where oil eventually collects after making its way through the engine). The pressure pump sucks oil directly from the oil pan and circulates it through the engine's oil galleries.

Dry Sump Systems
Dry sump systems store their oil in a separate tank, which feeds the pressure pump. Dry sump engines have a smaller oil pan which only serves as a sump, and a "scavenger pump" that drains the sump back into the main oil tank. They are termed "dry sump" systems because under normal operating conditions very little oil remains in the sump.

Note that there are other engineering differences in dry-sump systems, but they're largely beyond the scope of your question.
Illustrations thieved from https://www.slideshare.net/jesscar/piston-engines-oil.

One difference in distribution in a wet sump oil system is the inclusion of direct distribution from the sump by the splash method. This is especially true in some older reciprocating designs. See the AMT Powerplant Handbook.

@JonathanWalters Yes, that isn't well illustrated in the drawings above: In a wet sump design the crankshaft journals and counterweights will splash through the oil in the sump, kicking up oil (and creating a fine oily mist in the crankcase) to lubricate other components like the pistons. In a dry sump system the oil level in the sump may be below the arc of the crankshaft which reduces or eliminates splash lubrication. Dry sump engines often include "piston oilers" & other oil-squirting systems to supplement/replace the lost splash lubrication.


text:
Why do Computer Navigation Fixes still exist now that GPS waypoints can be used to define tracks?
A CNF is a point that defines a navigation track for a GPS, but why is it used when you there are GPS waypoints that are created to define a track?

From the AIM 1−1−17. Global Positioning System (GPS)

(2) A Computer Navigation Fix (CNF) is also a point defined by a
  latitude/longitude coordinate and is required to support
  Performance−Based Navigation (PBN) operations. The GPS receiver uses
  CNFs in conjunction with waypoints to navigate from point to point.
  However, CNFs are not recognized by ATC. … CNFs that do appear on
  aeronautical charts allow pilots increased situational awareness by
  identifying points in the aircraft database route of flight with
  points on the aeronautical chart. CNFs are random five-letter
  identifiers, not pronounceable like waypoints and placed in
  parenthesis. Eventually, all CNFs will begin with the letters “CF”
  followed by three consonants (for example, CFWBG).

As an example, the glide slope intercept for an ILS that I fly shows up in the Garmin 430 as a waypoint since the GPS requires a FAF to sequence to the MAP in order to conduct an approach. But it does not show up on the chart. (Remember that an ILS doesn’t have a FAF on the chart.) I have seen them on charts, but none come to mind right now.

Interesting thing about these "unpronouceable" fixes is that many of them ARE pronounceable, such as "AFWOX", northwest of BFF on V247.


text:
Why did the Boeing 787 design change shape from the original renderings to the actual design?
Here is a rendering of the original Boeing 787 design:

The plane built can be seen here:
787 as built http://images.franchiseherald.com/data/thumbs/full/3042/570/0/0/0/boeing-787-dreamliner.jpg
Why were the shapes of the nose, tailfin and tailcone changed during the design process?

Maybe for a less-awkward look.

The conceptual design was probably drawn by artists under the supervision of the marketing department, not engineers.

Your image links are broken.

Artwork is artwork. Airplanes are airplanes. The creation of the former does not drive the production of the latter.

According to this answer to the same question on Quora, it was changed in order to

keep as many parts common with other Boeing products as possible so they could reuse old part designs, vendors and tools and let the economics of scale help bring down the costs of these parts and thus the entire airplane.

By maintaining a greater similarity to previous Boeing products, the altered designs made the plane easier to design, build and sell, for a few reasons:

Maintaining similarity with older models made the certification process much easier and faster.
Instead of having to revise, test, remodel, and debug an entirely new part, the revised design had a greater background for the engineers to work with.
Completely new parts would have required more work building the machines used to construct the aircraft. Using prior designs led to reduced costs and time required in manufacturing.

Overall, the revised design made the aircraft easier and quicker to design and build which,  considering the issues and delays suffered by even the revised model, was a necessity.

authors: Bob Jarvis - Слава Україні


text:
Unlisted plane crash site in wilderness
I found what is probably a very old plane crash site but I am unable to find any info on it. When I search on maps of plane crash sites in the area, it would appear to be unlisted. How do I find further info on this before bothering anyone with something reported long ago. I got in about a half mile or so but it's in some very thick wilderness so I haven't completed the hike yet, but plan to soon. Maps seem to show 'wear' on the terrain around the area which is why I think this is an old crash site. It's location is 46°26'53.8"N 122°04'27.0"W. Any thoughts on the matter appreciated.

Why do you think there is a plane crash site there, if it is not listed and you have not been there?

I'm pretty sure that a crash of a plane of that size wouldn't pass unnoticed.

Intrerestingly the "plane" seems quite recent, it is not present in Bing Maps.

If it was real, it couldn’t be older than May 1980.

@300D7309EF17, it looks outside the blast zone to me.

I'm sorry but "I found" must have a different meaning for me. I was really confused about the answer to this question until I realized you were just browsing pictures online.

The image is from Google Maps, and that is where I "found it" as I was hiking in that area. Sorry that wasn't obvious enough. Thank you for your input.

That picture confused me, but it is simply a plane flying over that region when the satellite took a picture. You can see that is slightly blurred because it was in motion:

It is in the middle of different airways, not sure which one due to perspective (the LL circle is the position of the aircraft):

P.S. Good catch!

Of course! In motion. I feel silly haha. Well what fooled me is the trail cut in that parallels the forest road. All of this area including the forest road is jungle thick. If you pan out on maps you can see it looks like the parallel trail could've been cut for the purpose of getting to the plane had it actually been there. Lol! Thanks for taking the time to answer and saving me a good days hike to find nothing!

The Google Earth image in 3D mode was really confusing me, because the aicraft appears to follow the mountain slope...

The spaced colored images are typical of a moving airplane photographed by a satellite.  Here's a clearer example, with the airplane's deceleration matched by closer spacing.

Pretty sure an actual crashed plane of this size would not be nearly this intact.

For some reason this all makes me think of Mater's Ghost Lights ...


text:
How can you identify the upwind side of a thunderstorm, and why should you fly there?
When flying around a thunderstorm, it is advised that you fly in the upwind portion of the thunderstorm. First off, how do you figure out which side is the upwind and downwind of a thunderstorm? Second, why fly in the upwind?

The "anvil" of a Thunderstorm is always on the downwind side. Airline pilots routinely deviate around the upwind side in hopes of a smoother ride.
photo source: CRAZY CLOUDS: The Thunderstorm Anvil

Ahh, thank you. However, isn't the upwind side parallel to the downwind? Wouldn't you still be penetrating the anvil? If the left side of the thunderstorm is the upwind, wouldn't that side actually be a crosswind since the wind is blowing across?

@nyorkr23 I think you're confusing the term a bit. In this context, upwind is like saying upstream, it means the direction the wind is coming from. It's also relative - to the storm, upwind is to the left (in this picture) and downwind is to the right. So the aircraft could be upwind to this storm but at the same time be downwind to another one to the left of the picture. The aircraft will be experiencing a crosswind sure, but it is still on the upwind side of the storm cell. In the circuit, the upwind leg is parallel to the downwind one.

Oh I see. Its in relation to where the storm is moving, correct?

@nyorkr23: Just in case it isn't clear: "upwind" and "downwind" don't mean the same as "updraft" and "downdraft". The word "upwind" doesn't mean a wind that's blowing vertically upwards - it means "in the direction from which the wind is blowing", and "downwind" means "in the direction towards which the wind is blowing". For example: if you are downwind of a cheese factory, you will smell it, but if you are upwind of it, you won't. In the diagram in this answer, "upwind of the storm" is on the left of the diagram, because the wind is blowing left-to-right in that diagram.

@nyorkr23: From a more meteorological (less aviation) background... it's not so much primed on where the storm is moving towards (in fact, many storms are stationary... and while storms commonly do move similar to the wind at "upper-levels" (i.e. cruising altitudes) [since those winds are usually strongest], it's not guaranteed, as movement is a factor of wind at all levels, plus storm growth direction)

@nyorkr23 Believe you don't want to be in the downwind anvil area (right side of this diagram) because that's where the upper-level winds will tend to blow the updraft (the rising air in the middle of the storm) towards, which can be very intense (100 mph+ in strong storms), creating a lot of turbulence as it intersperses with portions of larger precipitation particles (even hail) creating downward motion.  Flying downwind may well be only slightly better than flying through the storm, despite the relatively tame appearance.

(Plus, indeed, flying downwind does still put you closer to the likely movement. It's very rare to see storms develop against the upper level winds (upwind if you like)). Meanwhile, downwind, you can get things like mammatus (see the formation causes), not where I'd like to be flying.  I see you have a question on this very topic

Also of note: very strong thunderstorms\supercells can even have a backsheared anvil (created by such a strong updraft that it expands against the wind). Doubt it'd be too great flying upwind at that point either (and perhaps the reason for the FAA directive). But the downwind side will still be clear because that is the largest part of the anvil. Storms with more symmetric anvils may well be in fairly light winds aloft.

You don't figure out which side of the storm (mature stage) has updrafts or downdrafts.  You simply don't fly near, in, or under a thunderstorm.  It's too dangerous.  The FAA advises that you stay at least 20NM away from intense radar echos associated with thunderstorms in order to avoid clear air turbulence and hailstones.  These factors may be present on all sides of a mature thunderstorm.

Yeah I get that. But if you were already near one and you can't avoid it because you screwed up, that's the scenario I'm talking about. The reason I ask is because a DPE asked this to a couple people I know and they tried to explain it, but I was confused.

That's all going to be dependent upon what the lifting factor creating the storm is.  For airmass thunderstorms forming over flat terrain on warm summer days, this may be very difficult to discern; for frontal storms, usually the air fwd of the front is rising and the air aft is falling.  At the point you are talking about, you probably will not have the option to pick where you want to penetrate the storm at;  if such time and luxury exist, you could probably maneuver to avoid or make a forced landing to get away from it.

How do you deal with the "line of storms spanning from Canada to Mexico" case then? Better to be on the ground wishing you were in the air, eh?

Don't take off in the first place.  A line of storms that size is an easily predictable thing and will be present on a proper pre-flight weather briefing.  This isn't a spontaneous thing; you would know about this long before you departed, therefore you have a lot of options available to you.

RIght but if you're flying a B777 on a 12 hour flight across the equator you're going to come across a thunderstorm more often than not. You don't stay on the ground in that scenario, you simply give it a wide berth, upwind if possible. In that case it's easy to determine which was is upwind because of onboard wind displays.

@Ben Dumb question: What principle do onboard wind displays work on?

@curious_cat Not dumb at all. It basically calculates the difference between TAS and GS. Here is an explanation: https://aviation.stackexchange.com/questions/23426/how-is-the-wind-direction-and-wind-speed-measured-in-flight

One reason that you stay away from the downwind side is hinted at by the funny quote by @psmears:

If you are downwind of a cheese factory, you will smell it, but if you
  are upwind of it, you won't.

Here is my take on it:

If you are downwind of a thunderstorm, you will get hit with hail, but if you
  are upwind of it, you won't.

Of course, it is possible there is no hail on the downwind side, but still it is a risk that is not usually necessary to take, and it is almost always possible to deviate as needed.
Below is an image taken from Professor Frank Ludlam's (Imperial College) 1961 article in Weather. The storm is moving right to left and affects are out to 20 km. You can see the large area of hail downwind.

I remember coming in to NAS Beeville in an A4 finishing up an instrument training hop. We were in a slow descent at 25k feet heading east at 250 kts. It was around sunset, with the sun behind and encroaching darkness in front of us. There were numerous large thunderstorm cells around us, some as high as 60-70k feet. As I looked up towards their tops I could see the lightning arcing from one side to the other of a cell in that weird, mesmerizing twilight. It was like a fireworks show, and quite impressive. There wasn't anybody out there that evening and we asked to deviate around weather. We got approval and did these lazy turns in our descent to the approach. One of those most pleasant fligths I visit often in my memory.

Simply put, flying downwind of thunderstorms increases your risk of hail.
The downwind portion of the thunderstorm is characterized by an anvil cloud. Typically the downwind side has a much higher probability of hail.
It is not uncommon for anvil clouds to extend a hundred miles down wind from larger cells.  Hail may be can be obscured by precipitation.  Hail can damage an aircraft even though other flight conditions such as turbulence are benign.


text:
Why couldn't my aircraft depart fully fueled on a 44C day?
My flight from Abudhabi to SFO was postponed. Official reason given to us was outside temperatures were too high - around 44+ degree Celsius and aircraft can not take off with full fuel loads at such high temperatures.
While sitting at terminal I saw other flights taking off. When I asked staff about those flights, answer was they are short haul - around 4-5 hours distance.
How does out side temperature affect these flights? Does it have anything to do with fuel volume changing with higher temperatures and hence wrong fuel consumption calculations?

Warmer air => Less air density => Less available thrust + Less lift => Decreased maximum take off weight.
A basic physic fact is that liquids volumes hardly depends on its temperature (it can vary a by a bit, but the difference is usually negligible). The issue is therefore not aboutt fuel volume changing

@pnuts It is about fuel and lift but your comment is kind of backwards. The actual reason is that, since warmer air means less lift, the plane can't take off at full weight. Because it can't take off at full weight, it can't have enough fuel on board to make a long-haul flight. The vast majority of the flight will be at air temperatures far below +44C, so having to burn more fuel at take-off to generate lift wouldn't be a huge deal; the problem is that the engines can't burn enough fuel to generate enough lift to take off.

There are two problems:
First, at higher temperatures, the air is less dense; therefore there is less oxygen (by mass) in every cubic metre of it; therefore more air must be ingested by the engine (by volume) for the same quantity of fuel to be completely burnt. If the intake flow rate of air is fixed, then less fuel can be burnt and less power developed compared to a colder air temperature.
The second problem is that the lower density of air reduces the lift generated by the aircraft's wings at any speed. To make up for this the aircraft can travel faster.
In practise this means that aircraft operating in "hot and high" conditions—altitude also affects air density—will require longer runways to take off.
If it gets too hot then the aircraft might not have enough runway to get airborne.
For safety reasons the runway must be long enough for the aircraft to come to a stop if the commander decides to reject the take off at the last moment. But fast, heavy aircraft take a long time to stop; so this means the runway must be even longer.
If the aircraft is lightly loaded then it is not such a problem; there is less mass to accelerate and a lower speed must be obtained for take off. Thus a short flight simply takes a bit longer but still gets off the ground. But for AUH-SFO, this is a very long flight and will require a great deal of fuel to be taken onboard (at a guess I would imagine something on the very rough order of 80 tons). The specifics will vary by aircraft, and by how much is on them.
https://en.wikipedia.org/wiki/Hot_and_high

I can definitely confirm this.  I live in a climate that can be very hot in the summer and we occasionally get cases of planes having to leave some passengers behind because of "weather" when it's sunny out.  We don't get cancellations because there are other airports around, they can always put down for fuel if they have to.  For an overwater flight, though, I could easily see a cancellation.

For jet aircraft, the first "problem" is a non-problem. if density altitude were an issue for the turbojets in modern jetliners, then they would not be able to fly at 40,000+ feet. The FADEC and the compressor of the jet engine mix the fuel in the proper proportion for the density altitude.

@rbp -- the OAT and power demand (i.e. fuel flows needed) are both far lower at altitude than they are during a T/O.

@UnrecognizedFallingObject yes, but that's not what OP wrote: more air must be ingested by the engine (by volume) for the same quantity of fuel to be completely burnt.

@rbp In what sense is this untrue? If take off engine performance is not affected by air temperature I can delete this answer.

you're describing what happens in a piston engine, not a turbine. a turbine has a compressor section and a FADEC which precisely controls the air-to-fuel mixture based on the density altitude

'oxygen flux' is not an english phrase, so I don't know what you mean. and writing an uniformed answer is not the place 'to learn more about this'.

I recommend you learn about gas turbines. They are managed via "interstage turbine temperature" (ITT) not "outside air temperature" (OAT). Peace out

@rbp: Fact is, trust will be less at higher temperature. Limiting the take-off in most cases is the remaining climb speed with one engine inoperative. Above a certain temperature and aircraft mass it will be impossible to survive an engine failure above v1. Either mass or OAT must be lowered for the flight to take off safely.

@rbp, you are accidentally right that “more air must be ingested … by volume … fuel to be completely burnt” is wrong, because turbines work with excess air and this is not the limiting factor. However, lower density still does limit the thrust, due to RPM limit (at lower density, the same RPM gives lower mass flow) and due to temperature limit (you can add less heat to an already hot air before it becomes too hot for the turbine). So hot and high is very much a problem for turbine aircraft. The reason is just somewhat different from spark-ignited engines.

Does it have anything to do with fuel volume changing with higher temperatures and hence wrong fuel consumption calculations?

I doubt wrong fuel consumption calculations are involved, but fuel density is a limiting factor for some aircraft, both insofar as limiting takeoff weight and possibly prohibiting takeoff. For example, for a 747-400BCF, a minimum fuel density of 6.0 lbs/gal is required up to 820,000 lb. From 820,000 lbs to 870,000 lbs the minimum changes linearly from 6.0 to 6.43. From 820,000 to 870,000 there are also takeoff centre of gravity (CG) restrictions. The CG must be forward of 19.1% MAC1 at 820,000 changing linearly to 19.5% MAC at 850,000, then linearly to 20.0% MAC at 870,000.
If you wish to see this graphically displayed, go to section 1-05-001 of the manual at http://terryliittschwager.com/WB/manuals/Boeing_747-400BCF_GPR1_WBM.pdf, pdf page 69 for lbs, 70 for kgs.
Also some aircraft have a prohibition against operation in ambient temperatures above a certain point. I seem to remember to remember 54 Celsius for 747-100 and -200 aircraft, but don't hold me to that.

1MAC = Mean Aerodynamic Chord of the wing. The position of the CG is usually expressed as a percentage of the MAC where 0% is the leading edge and 100% is the trailing edge.

What is CG? Centre of gravity? And MAC? Thanks

@Calchas You are correct, CG is center of gravity. MAC is Mean Aerodynamic Chord. The longitudinal CG of large aircraft is usually expressed in terms of the percentage of the Mean Aerodynamic Chord. Thus if the CG is 20.0, what they're saying is that it's 20% of the way from the leading edge of the MAC to the trailing edge. The CG enters into many limitations. What the MAC actually is, is considerably more complicated, but think of it as the distance from from the leading edge of the wing to the trailing edge if the wing was of a constant distance from leading edge to trailing edge.

The way I think of MAC is that it identifies the relative position between the Center of Pressure and the Center of Gravity. For longitudinal stability, the CG has to be further forward than the CP. Both of these can be expressed as %MAC.

There are a lot of complex answers to a rather simple question.
As others have mentioned, the pressure of air decreases as temperature increases.  This means the fuel in the tanks is being less compressed by the air pressure, thus the fuel makes up for this by taking up a larger volume for a specific mass.
Jet airliners measure fuel consumption in mass, opposed to volume.  So whilst the volume remains constant, environmental conditions can alter the amount of mass it takes to fill that volume.  Simply put, a "full" tank (considered by volume) would weigh more on a cold day than on a hot one.

Mostly true, but it isn't the pressure of air decreasing which makes the fuel less compressed.  It is simply the fuel expanding due to its own temperature increase.  This happens no matter what the temperature is in the air around the fuel (particularly noticeable when fueling from underground tanks and the fuel is significantly cooler than the ambient temperature).


text:
How do you apply to offer WINGS credit for an event you are sponsoring?
Douglas Rotary is sponsoring a fly-in October 3, 2015 in Douglas, AZ at the Douglas Muni. Airport.  How do we apply to get pilots WINGS credit for their training?

A fly-in by itself doesn't usually qualify for WINGS credit, but if you're also running educational programs or seminars there's a good chance you've got something that will qualify.
Normally you'd work with a FAA Safety Team representative to help set up the program so it meets the WINGS credit requirements (they have access to premade presentations, slides/videos, and with a little notice they can usually help find presenters/speakers), and the representative will then coordinate with your regional FAA Safety Team manager to get the programs listed in SPANS so people can sign up and receive credit.
If you have an account on faasafety.gov you can search the FAASTeam directory for representatives near you:

(I did a cursory search and I didn't see anyone in Douglas, but there are a few folks in Tuscon.)
If you can't get in touch with any of the representatives your best bet is to contact your local FSDO (Scottsdale in your case) directly and ask for the "FAA Safety Team Program Manager" - they'll be able to work with you to get the program coordinated and set up in SPANS.

If you intend to do regular events with safety programs it would probably be worth getting yourself or someone else in your group set up as a FAASTeam representative. There's some (really simple/basic) training involved, and usually the regional program manager or one of the lead representatives in your area will want to meet with you just so they know what you look like, and once you're set up you'll be able to submit requests to have your programs listed directly.

There's nothing that I can find on the FAA website about this. There is a document called Administering WINGS and awards programs but it doesn't have any useful information that I can see about how to host or sponsor a WINGS credit event.
So, in the absence of a published process for requesting approval, I'd simply contact FAASafety directly and ask them.


text:
Can I fly internationally as a commercial pilot, without an ATP certificate?
Are commercial pilots allowed to fly internationally? Are Commercial Pilots required to take an Airline Transport Pilot (ATP) program/training to fly internationally? And is a commercial pilot the same as an airline pilot?

The last part of the question (whether a CPL is the same as an ATPL) might be better posted as a separate question.

A US rated pilot (private, commercial or ATP) can operate an N- registered airplane anywhere on earth (subject to the persons ability or inability to enter certain countries airspace).
At the regional airlines it was common that the first officer only possessed a commercial certificate (the full ATP is earned during the pilots first upgrade training to become a captain).  These first officers will have no restriction on international travel based on their certificate and can operate international flights. These days FOs will have restricted ATPs rather than commercial certificates, but this is unrelated to the ability to operate internationally.
Outside of airlines you'll find positions where the only a commercial certificate is necessary and these pilots can operate internationally.
If the airplane in question requires a type rating then if the copilot does not have a full type rating, they will need an "SIC type" to operate internationally. This stems from an ICAO requirement that both pilots be type rated. The SIC type can be added to a private or commercial certificate, not just an ATP so this won't be a restriction based on certificate level.

Doesn't the US now require an ATP-restricted for FOs in scheduled service?

Your comment made me do some research on the topic (since I knew barely anything on it) and it seems, that there is now a "restricted ATP" license. This text here http://www.aopa.org/News-and-Video/All-News/2013/July/10/FAA-releases-final-ATP-certification-rule.aspx does, however, not specify if it is REQUIRED for FOs' scheduled services or if it LIMITS the holder to the FO position in scheduled services while it is no requirement. Yet, as I understood the article, the first interpretation seems more likely (restricted ATP license as requirement for FO in scheduled services)

@cpast Thanks, I wasn't aware of that change. I've edited to include that info.


text:
Why are aircraft designed so that the wing stalls before the tail?
I read somewhere that conventional aircraft are designed so that the main wing always stalls before the tailplane. Why is that?
My concern is that if the wing stalls, suddenly the tail will push the aircraft into a higher AoA, and maybe stall itself, though the pilot would still have control for some time to avoid that. On the other hand, if the tail stalls, the plane will (violently?) pitch down, but would be able to recover afterward.
So what am I missing?
Edit: Assume the center of gravity of the plane is in front of the main wing

this question doesn't make any sense without disclosing where the CG is.

You are missing the weight force. The wing should stall first because then it will produce less lift and the weight will make the aircraft pitch down.
In attached flow, the lift from wing and tail is balanced such that the combined resulting force is acting exactly at the longitudinal position of the center of gravity. If the wing stalls, the balance of lift is shifted backwards (regardless of the tail producing lift or a downforce), because now the forward part of the wing-tail-combination will produce proportionally less lift than it did in attached flow. The center of gravity will then be ahead of the resulting lift force and will pull the nose of the aircraft down.
A tail stall is bad news for the pilot and should be avoided:

A stalled tail will have much less elevator effectivity, reducing the control power available to the pilot
A stalled tail at high angle of attack is stalling at maximum lift, so it produced positive lift before. If it stalls, its lift will shrink and make the aircraft pitch up.

In a conventional configuration the tail flies in the flow field of the wing. Because the wing's downwash increases with angle of attack, the angle of attack variations at the tail are reduced. This helps to keep the flow at the tail attached over the whole useable angle of attack range of the wing. A tail stall is either caused by a wrong location of the center of gravity (CG) or by a very poor transsonic design which causes shock-induced stalling of the tail when the wing is still doing fine. Very rarely can you stall the tail by a wrong trim setting when a moveable stabilizer is used for trimming, or in a deep stall.
Some supersonic aircraft compensate for the backward shift of the center of lift in supersonic flow by pumping fuel from forward to rear. If an airplane with such a rear CG location slows down to subsonic speed, it will need to produce proportionally more lift with the tail than with the wing. If it now pitches up (say, for a tight turn) it will risk a tail stall. Note that such a configuration is aerodynamically unstable at subsonic speed.

EDIT:
Now you define the center of gravity as ahead of the wing, which makes for a very stable configuration. The tail is producing a downforce to compensate the pitch-down action of the wing's lift.
If the wing stalls first, lift will become less than weight and the aircraft will accelerate downwards. Now the angle of attack will increase at both the tail and the wing; at the tail even for two reasons:

The downward acceleration will change the local flow direction to a larger angle of attack, and
The diminished downwash from the wing will cause an angle of attack increase of its own at the tail. This effect takes a little longer to manifest itself: The delay is the distance between the quarter points of tail and wing divided by the airspeed.

Both effects will quickly create a dominant pitch-down moment for the aircraft because the tail will contribute much less downforce than before the stall, and the diminished pitch-down moment of the wing will become insignificant.

I edited my question so that you guys know what I was imagining (c.g. is in front of the wing). So wing produces negative pitching moment, as soon as it stalls there is a net positive moment and the aircraft pitches up more.

@Jacob: Stall does not equal zero pitching moment. Normally, in a stall the forward part of the airfoil loses more lift and the center of pressure moves back, increasing the negative pitching moment. However, the wing's pitching moment is small when compared to that of the tail. It will dominate the pitch moment in a stall regardless of CG position.

@Jacob: Now I get what you mean: The wing will produce less lift and less pitch-down moment for the full aircraft. But in a stall lift is lower than weight, and the whole aircraft will accelerate downwards. Now the tail will produce even less downforce and pitch the aircraft down.

Yup that's what I was looking for! Neglected the downward acceleration. Thanks!


text:
Why was brown chosen to represent the ground side of an attitude indicator?
Is there any particular reason for having the ground represented by brown on an artificial horizon or PFD?
Blue represents sky, brown represents earth, which will be used for easily identifying the aircraft attitude (along with line of origin). Using blue to represent the sky makes conventional sense. But why is brown used? Is there any scientific reason for using brown instead of another color?

I would also note that this is definitely not unique to PFDs. It's been used on attitude indicators since long before PFDs existed. The digital attitude indicators on PFDs were just designed to look like the analog attitude indicators that pilots were already accustomed to.

The answer to the specific question of "why PFD's (glass cockpits) use this standard" is because their old style gauge cockpits used it before them. The glass cockpits of today are made to be similar to the older gauges so as to avoid confusion in their operation when moving from one type of aircraft to the other. This has been shown to be an issue in the past in the difference between American and Russian attitude indicators as such instrument operation strives to be at least somewhat uniform.
Now as for the more general question "why are attitude indicators Blue/Brown?" there are a few reasons. First off some types of color blindness cause issues with the blue/green mix making it a combination to avoid (some info on color blind flying). Second, and perhaps as important is that blue and brown sit basically on opposite sides of the color wheel making them very contrasty while blue and green sit right next to each other on the wheel. This ensures accurate viewing in most lighting situations.
There are also other attitude indicators like those commonly used in military aircraft which have had different colors

(source)
The oldest examples are completely void of any color (you can see why they introduced color)

(source)
For what its worth some modern flight displays now include terrain data and are capable of showing many other colors to outline it as can be seen here on this Garmin unit

(source)

If they used green (like grass) you would have asked the same: "Why didn't the use brown (like soil)?"
Blue - brown is easier to distinguish, than blue - green, blue - red or another color-combination you can think of.
Contrast:
The use of this two colors can be explained by the high contrast from blue to brown. The pilot can find out with one quick glance at the PFD how the aircraft is positioned in the air.
Natural colors - pilot instantly knows what it means:
Because those are "natural" colors, the pilot instantly knows that blue means sky and brown means ground. He doesn't have to process the color information in his head just to find out what it means. This would take much longer.

BTW, most of the geographical places natural colour of soil is black.

@Lucky care to make some examples? I can't think of a single one. (and in photos from space you don't see vast swathes of black)

@Lucky I don't think Black is a good choice for the ground-part of the PFD... How will you iluminate it at night? Just pointing out the problems ;)

@Federico Areas around volcanos often have black 'soil' (if it's fair to call volcanic rock 'soil,') to the point that volcanic islands often have black sand beaches. Of course, you're right, though, that the vast majority of soil is not black.

I agree with @jklingler, but some part of ground is brown and some part is black and majority is back soil Federico.. Refer India, North part of Karnataka

You may be correct with your "majority is black"-thing, but every child can associate brown = ground. Black is no option for the ground-part of an PFD.


text:
Can I fly in the USA with an FAA ATP, if I don't have a commercial certificate?
I am Taiwanese and I have an FAA ATPL, but I don't have an FAA CPL.
Can I fly commercial operations in the US?

I'm curious, how did you obtain an FAA ATP?

@digitgopher you can apply for the FAA ATP with a foreign commercial certificate with instrument privileges.

Maybe. Your ATP certificate does give you commercial privileges, as per 14 CFR 61.167:

(a) Privileges. (1) A person who holds an airline transport pilot
  certificate is entitled to the same privileges as a person who holds a
  commercial pilot certificate with an instrument rating.

But, that doesn't authorize you to work in the USA or even to enter the USA, which is an entirely different question about immigration law. As a foreigner, you'll need an appropriate visa or a green card in order to be legally employed and paid. You can ask more about that on another site.

Yes.  If you have an ATP in the US it comes with all the privileges of a commercial license including flying for a 121 / 135 operator.
See 61.167:

(a) Privileges. (1) A person who holds an airline transport pilot
  certificate is entitled to the same privileges as a person who holds a
  commercial pilot certificate with an instrument rating.